The present invention is directed generally to a method of separating gases in a fluorescent lamp, and more particularly to a method of analyzing mercury in a fluorescent lamp.
In a mercury fluorescent lamp, light is generated by producing an electrical discharge in a tube filled with a mixture of mercury and an inert gas. The electrical discharge excites the mercury atom causing an outer shell electron to jump to a higher orbit. When the excited electron returns to its former energy level, it gives up energy in the form of ultraviolet radiation. This radiation is absorbed by a fluorescent phosphor coating on the inside of the lamp tube and re-radiated as visible light.
When manufacturing a fluorescent lamp tube, a small drop of liquid mercury is inserted into the lamp tube, an inert gas, typically argon, neon, xenon, krypton or a mixture thereof is charged into the tube and the tube is then sealed. Typically, a large excess of mercury is put in the tube in order to control the vapor pressure with an excess of mercury. For example, U.S. Pat. Nos. 3,309,565 and 4,529,912 teach that the vapor pressure of mercury is determined by the coldest portion of the bulb and therefor the optimum vapor pressure can be achieved by controlling the temperature of a spot on the lamp tube. U.S. Pat. No. 5,882,237 teaches that the vapor pressure of mercury can be controlled by forming a mercury zinc amalgam with excess mercury. U.S. Pat. No. 5,909,085 teaches controlling the vapor pressure by a combination of thermal control and amalgam formation. These patents do not teach condensing all the mercury or analyzing bound or available mercury.
It is known that the luminosity of a fluorescent lamp is a function of the vapor pressure of the mercury during operation. It is also known that the vapor pressure of mercury in the light tube is a function of the temperature of the tube. The maximum luminosity of a fluorescent lamp is typically achieved at a pressure of approximately 6-7 milliTorr (mtorr) which is generated at a temperature of approximately 40xc2x0 C. Deviation from this pressure, either above or below, results in reduced luminosity. It is therefore desirable to have enough mercury in the tube to generate a partial pressure of about 7 mtorr. From an economic and environmental standpoint, however, it is preferable to have as small an excess of mercury in the tube as possible. Therefore, providing excess mercury to achieve the desired mercury partial pressure is not desirable.
The prior art methods of controlling the mercury vapor pressure using excess mercury result in an inefficient use of mercury and reduced lamp luminosity. Therefore, it would be desirable to obtain an accurate method of measuring the distribution of mercury in the lamp tube to obtain improved lamp luminosity while using as little excess mercury as possible.
The invention relates to a method of condensing a gas comprising: cooling at least a first portion of a vessel containing a first gas below a condensation temperature of said first gas; maintaining the temperature of said first portion of said vessel below the condensation temperature until said first gas condenses on a surface of at least a second portion of said vessel; removing said second portion of said vessel, said second portion containing the condensed first gas; and analyzing at least one of said condensed first gas or the bound first gas.
The invention also relates to a method of manufacturing a fluorescent lamp, comprising: cooling at least a first portion of a test lamp below the condensation temperature of mercury contained in said test lamp while operating said test lamp; maintaining the temperature of said first portion below the condensation temperature of said mercury until substantially all the available mercury contained in the test lamp condenses on the surface of at least the first portion of said test lamp; removing a second portion of said lamp, said second portion containing the condensed mercury; and analyzing at least one of said condensed mercury or the bound mercury remaining in the test lamp to determine the amount of available or bound mercury present in the lamp; and placing a first amount of mercury into at least a first fluorescent lamp based on the amount of available mercury determined during the analyzing step.
FIG. 1 is a graph showing luminosity as a function of temperature.
FIG. 2 is a graph showing luminosity as a function of mercury pressure.
FIG. 3 is graph of the consumption of mercury as a function of time for a typical lamp.
FIG. 4 is a side view of a preferred embodiment of the invention.
FIG. 5 is an enlarged view of a section of the tube of FIG. 4.
FIG. 6 is an enlarged view of a section of the tube of FIG. 4.
FIG. 7 is a side view of a preferred embodiment of the invention.
FIG. 8 is a side view of a preferred embodiment of the invention.
FIG. 9 is a side view of a preferred embodiment of the invention.